The ionisation constant of a weak acid $(HA)$ in terms of molar conductivity at infinite dilution $(\Lambda _m^\infty)$ and molar conductivity at concentration $C$ $(\Lambda _m)$ is given by:

• A
  $K_a = \frac{C\Lambda _m^\infty}{(\Lambda _m - \Lambda _m^\infty)}$
• B
  $K_a = \frac{C\Lambda _m^2}{\Lambda _m^\infty (\Lambda _m^\infty - \Lambda _m)}$
• C
  $K_a = \frac{C(\Lambda _m^\infty)^2}{\Lambda _m^\infty (\Lambda _m - \Lambda _m^\infty)}$
• D
  None of these